1. Field of Invention
The present invention relates generally to supplying compressed gas and, more particularly, to a device which uses a relatively high pressure gas to produce a supply of lower pressure gas.
2. Description of the Related Art
Over the years, a variety of devices have been introduced which control the pressure of extremely high pressure compressed air and other gasses. One such device is a regulator. A regulator includes a controllable resistive aperture which is typically set to keep the output pressure (or flow rate) constant. In the resistive aperture, the high pressure air expands and converts its potential energy into kinetic energy. It also cools as it expands. At the far end of the regulator, the high velocity air is slowed by friction. The kinetic energy is converted to heat which warms the air back up. The exhaust temperature of a regulator is close to the intake temperature. Although regulators are relatively inexpensive and lightweight, they are also very energy inefficient. The potential energy difference between the intake and output gas is wasted as heat. As a result, they are typically used only to buffer gas flow in situations where energy conservation is not important.
Some commercial hydraulic equipment utilizes high pressure air with greater efficiency than a regulator. An example of this type of equipment is a dive shop compressor which is used to compress air to 2250 to 3000 PSI for use in SCUBA tanks. One can imagine the compressor being used in reverse as a compressed air motor which could be used to drive a high volume, low pressure air compressor. This type of compressor is, however, large and costly. A typical dive shop compressor capable of 30 horsepower and, possibly, 80% efficiency weighs upwards of 500 lbs. for the air handling section alone and costs $40,000 (the electric motor would add additional weight and cost). Such compressors also require extensive maintenance in that they need special oil and periodic seal replacement. They also have a relatively poor power to weight ratio.
Much of the expense and weight associated with hydraulic equipment is associated with the sliding seals. In order to operate under relatively high pressures, the seals must have very smooth surfaces, which requires expensive low tolerance machining. The sliding surfaces must also mate closely. Such mating requires thick, heavy pieces of metal that will not deform under the forces involved. To make up for imperfections in the machining process, a high viscosity oil is used. The high viscosity oil limits the speed of the high pressure compressor.
U.S. Pat. No. 5,174,130 discloses a compressor which uses an acoustical standing wave to compress refrigerant. The standing wave in this compressor has the same area at both nodes giving it the same pressure at both nodes. The wave is powered by electrical means and cannot be used as an energy transforming device.